Ultimately, the division was made in 1412: Jan I retained Żagań, and one year later (in 1413) he also took possession over the duchy of Przewóz in the Polish-German border area (obtained as a result of his marriage with Scholastika, a daughter of Elector Rudolph III).
Three years later, John participated with his brothers in the negotiations between the emperor and Teutonic Knights in Preszburg (now Bratislava), where it was decided go to war against Poland.
At the same time, in connection with the growing power of the Hussites, the Duke of Żagań decided to pay them high contributions, which was to ensure the safety of his lands.
After the death of Emperor Sigismund, Jan I stood on the side of his son-in-law Albert V of Habsburg, and on 3 December 1438 he paid tribute to him in Wroclaw.
Because of these events, in contemporary sources he was considered a cruel man and even a sadist, as was further described in the Roczniku Głogowskim: when he had sexual relations with his wife he tended to sharpen his spurs.